<!DOCTYPE html>
<html lang="zh-CN">
<head>
  <meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1, maximum-scale=2">
<meta name="theme-color" content="#222">
<meta name="generator" content="Hexo 3.9.0">
  <link rel="apple-touch-icon" sizes="180x180" href="/images/apple-touch-icon-next.png">
  <link rel="icon" type="image/png" sizes="32x32" href="/images/favicon-32x32-next.png">
  <link rel="icon" type="image/png" sizes="16x16" href="/images/favicon-16x16-next.png">
  <link rel="mask-icon" href="/images/logo.svg" color="#222">

<link rel="stylesheet" href="/css/main.css">

<link rel="stylesheet" href="https://fonts.loli.net/css?family=Lato:300,300italic,400,400italic,700,700italic&display=swap&subset=latin,latin-ext">
<link rel="stylesheet" href="/lib/font-awesome/css/all.min.css">

<script id="hexo-configurations">
    var NexT = window.NexT || {};
    var CONFIG = {"hostname":"monocy.gitee.io","root":"/","scheme":"Gemini","version":"7.8.0","exturl":false,"sidebar":{"position":"left","display":"post","padding":18,"offset":12,"onmobile":false},"copycode":{"enable":true,"show_result":true,"style":"mac"},"back2top":{"enable":true,"sidebar":true,"scrollpercent":true},"bookmark":{"enable":false,"color":"#222","save":"auto"},"fancybox":false,"mediumzoom":true,"lazyload":true,"pangu":false,"comments":{"style":"tabs","active":"valine","storage":true,"lazyload":true,"nav":null,"activeClass":"valine"},"algolia":{"hits":{"per_page":10},"labels":{"input_placeholder":"Search for Posts","hits_empty":"We didn't find any results for the search: ${query}","hits_stats":"${hits} results found in ${time} ms"}},"localsearch":{"enable":true,"trigger":false,"top_n_per_article":5,"unescape":false,"preload":false},"motion":{"enable":true,"async":false,"transition":{"post_block":"fadeIn","post_header":"slideDownIn","post_body":"slideDownIn","coll_header":"slideLeftIn","sidebar":"slideUpIn"}},"path":"search.xml"};
  </script>

  <meta name="description" content="前言近期开始学习 Node 和 MySQL 相关的知识了，项目也开始从纯前端转向了“全栈”（刚刚起步）。起初还是挺痛苦的，特别是数据库设计和查询，大学学习的东西基本都还回去了，不过在一次次问题中也渐渐总结了些经验，这里就记录一下“初学者”难免会遇到的一些问题。">
<meta name="keywords" content="数据库,Mysql">
<meta property="og:type" content="article">
<meta property="og:title" content="Mysql 的小技巧">
<meta property="og:url" content="https://monocy.gitee.io/2020/06/09/Mysql-的小技巧/index.html">
<meta property="og:site_name" content="沐光">
<meta property="og:description" content="前言近期开始学习 Node 和 MySQL 相关的知识了，项目也开始从纯前端转向了“全栈”（刚刚起步）。起初还是挺痛苦的，特别是数据库设计和查询，大学学习的东西基本都还回去了，不过在一次次问题中也渐渐总结了些经验，这里就记录一下“初学者”难免会遇到的一些问题。">
<meta property="og:locale" content="zh-CN">
<meta property="og:updated_time" content="2022-07-26T13:09:59.035Z">
<meta name="twitter:card" content="summary">
<meta name="twitter:title" content="Mysql 的小技巧">
<meta name="twitter:description" content="前言近期开始学习 Node 和 MySQL 相关的知识了，项目也开始从纯前端转向了“全栈”（刚刚起步）。起初还是挺痛苦的，特别是数据库设计和查询，大学学习的东西基本都还回去了，不过在一次次问题中也渐渐总结了些经验，这里就记录一下“初学者”难免会遇到的一些问题。">

<link rel="canonical" href="https://monocy.gitee.io/2020/06/09/Mysql-的小技巧/">


<script id="page-configurations">
  // https://hexo.io/docs/variables.html
  CONFIG.page = {
    sidebar: "",
    isHome : false,
    isPost : true,
    lang   : 'zh-CN'
  };
</script>

  <title>Mysql 的小技巧 | 沐光</title>
  






  <noscript>
  <style>
  .use-motion .brand,
  .use-motion .menu-item,
  .sidebar-inner,
  .use-motion .post-block,
  .use-motion .pagination,
  .use-motion .comments,
  .use-motion .post-header,
  .use-motion .post-body,
  .use-motion .collection-header { opacity: initial; }

  .use-motion .site-title,
  .use-motion .site-subtitle {
    opacity: initial;
    top: initial;
  }

  .use-motion .logo-line-before i { left: initial; }
  .use-motion .logo-line-after i { right: initial; }
  </style>
</noscript>

</head>

<body itemscope itemtype="http://schema.org/WebPage">
  <div class="container use-motion">
    <header class="header" itemscope itemtype="http://schema.org/WPHeader">
      <div class="header-inner"><div class="site-brand-container">
  <div class="site-nav-toggle">
    <div class="toggle" aria-label="切换导航栏">
      <span class="toggle-line toggle-line-first"></span>
      <span class="toggle-line toggle-line-middle"></span>
      <span class="toggle-line toggle-line-last"></span>
    </div>
  </div>

  <div class="site-meta">

    <a href="/" class="brand" rel="start">
      <span class="logo-line-before"><i></i></span>
      <h1 class="site-title">沐光</h1>
      <span class="logo-line-after"><i></i></span>
    </a>
      <p class="site-subtitle" itemprop="description">记录在前端之路的点点滴滴</p>
  </div>

  <div class="site-nav-right">
    <div class="toggle popup-trigger">
        <i class="fa fa-search fa-fw fa-lg"></i>
    </div>
  </div>
</div>




<nav class="site-nav">
  <ul id="menu" class="main-menu menu">
        <li class="menu-item menu-item-home">

    <a href="/" rel="section"><i class="fa fa-home fa-fw"></i>首页</a>

  </li>
        <li class="menu-item menu-item-about">

    <a href="/about/" rel="section"><i class="fa fa-user fa-fw"></i>关于</a>

  </li>
        <li class="menu-item menu-item-tags">

    <a href="/tags/" rel="section"><i class="fa fa-tags fa-fw"></i>标签<span class="badge">31</span></a>

  </li>
        <li class="menu-item menu-item-categories">

    <a href="/categories/" rel="section"><i class="fa fa-th fa-fw"></i>分类<span class="badge">15</span></a>

  </li>
        <li class="menu-item menu-item-archives">

    <a href="/archives/" rel="section"><i class="fa fa-archive fa-fw"></i>归档<span class="badge">61</span></a>

  </li>
      <li class="menu-item menu-item-search">
        <a role="button" class="popup-trigger"><i class="fa fa-search fa-fw"></i>搜索
        </a>
      </li>
  </ul>
</nav>



  <div class="search-pop-overlay">
    <div class="popup search-popup">
        <div class="search-header">
  <span class="search-icon">
    <i class="fa fa-search"></i>
  </span>
  <div class="search-input-container">
    <input autocomplete="off" autocapitalize="off"
           placeholder="搜索..." spellcheck="false"
           type="search" class="search-input">
  </div>
  <span class="popup-btn-close">
    <i class="fa fa-times-circle"></i>
  </span>
</div>
<div id="search-result">
  <div id="no-result">
    <i class="fa fa-spinner fa-pulse fa-5x fa-fw"></i>
  </div>
</div>

    </div>
  </div>

</div>
    </header>

    
  <div class="reading-progress-bar"></div>

  <a href="https://github.com/kazehaiya" class="github-corner" title="Follow me on GitHub" aria-label="Follow me on GitHub" rel="noopener" target="_blank"><svg width="80" height="80" viewBox="0 0 250 250" aria-hidden="true"><path d="M0,0 L115,115 L130,115 L142,142 L250,250 L250,0 Z"></path><path d="M128.3,109.0 C113.8,99.7 119.0,89.6 119.0,89.6 C122.0,82.7 120.5,78.6 120.5,78.6 C119.2,72.0 123.4,76.3 123.4,76.3 C127.3,80.9 125.5,87.3 125.5,87.3 C122.9,97.6 130.6,101.9 134.4,103.2" fill="currentColor" style="transform-origin: 130px 106px;" class="octo-arm"></path><path d="M115.0,115.0 C114.9,115.1 118.7,116.5 119.8,115.4 L133.7,101.6 C136.9,99.2 139.9,98.4 142.2,98.6 C133.8,88.0 127.5,74.4 143.8,58.0 C148.5,53.4 154.0,51.2 159.7,51.0 C160.3,49.4 163.2,43.6 171.4,40.1 C171.4,40.1 176.1,42.5 178.8,56.2 C183.1,58.6 187.2,61.8 190.9,65.4 C194.5,69.0 197.7,73.2 200.1,77.6 C213.8,80.2 216.3,84.9 216.3,84.9 C212.7,93.1 206.9,96.0 205.4,96.6 C205.1,102.4 203.0,107.8 198.3,112.5 C181.9,128.9 168.3,122.5 157.7,114.1 C157.9,116.9 156.7,120.9 152.7,124.9 L141.0,136.5 C139.8,137.7 141.6,141.9 141.8,141.8 Z" fill="currentColor" class="octo-body"></path></svg></a>


    <main class="main">
      <div class="main-inner">
        <div class="content-wrap">
          

          <div class="content post posts-expand">
            

    
  
  
  <article itemscope itemtype="http://schema.org/Article" class="post-block" lang="zh-CN">
    <link itemprop="mainEntityOfPage" href="https://monocy.gitee.io/2020/06/09/Mysql-的小技巧/">

    <span hidden itemprop="author" itemscope itemtype="http://schema.org/Person">
      <meta itemprop="image" content="/images/avatar.jpg">
      <meta itemprop="name" content="蔡胤">
      <meta itemprop="description" content="Just do IT!">
    </span>

    <span hidden itemprop="publisher" itemscope itemtype="http://schema.org/Organization">
      <meta itemprop="name" content="沐光">
    </span>
      <header class="post-header">
        <h1 class="post-title" itemprop="name headline">
          Mysql 的小技巧
        </h1>

        <div class="post-meta">
              <span class="post-meta-item">
                <span class="post-meta-item-icon">
                  <i class="far fa-calendar-check"></i>
                </span>
                <span class="post-meta-item-text">更新于</span>
                <time title="修改时间：2022-07-26 21:09:59" itemprop="dateModified" datetime="2022-07-26T21:09:59+08:00">2022-07-26</time>
              </span>
            <span class="post-meta-item">
              <span class="post-meta-item-icon">
                <i class="far fa-folder"></i>
              </span>
              <span class="post-meta-item-text">分类于</span>
                <span itemprop="about" itemscope itemtype="http://schema.org/Thing">
                  <a href="/categories/数据库/" itemprop="url" rel="index"><span itemprop="name">数据库</span></a>
                </span>
            </span>

          
  
  <span class="post-meta-item">
    
      <span class="post-meta-item-icon">
        <i class="far fa-comment"></i>
      </span>
      <span class="post-meta-item-text">Valine：</span>
    
    <a title="valine" href="/2020/06/09/Mysql-的小技巧/#valine-comments" itemprop="discussionUrl">
      <span class="post-comments-count valine-comment-count" data-xid="/2020/06/09/Mysql-的小技巧/" itemprop="commentCount"></span>
    </a>
  </span>
  
  
            <span class="post-meta-item" title="本文字数">
              <span class="post-meta-item-icon">
                <i class="far fa-file-word"></i>
              </span>
                <span class="post-meta-item-text">本文字数：</span>
              <span>1.8k</span>
            </span>
            <span class="post-meta-item" title="阅读时长">
              <span class="post-meta-item-icon">
                <i class="far fa-clock"></i>
              </span>
                <span class="post-meta-item-text">阅读时长 &asymp;</span>
              <span>2 分钟</span>
            </span>

        </div>
      </header>

    
    
    
    <div class="post-body" itemprop="articleBody">

      
        <h3 id="前言"><a href="#前言" class="headerlink" title="前言"></a>前言</h3><p>近期开始学习 Node 和 MySQL 相关的知识了，项目也开始从纯前端转向了“全栈”（刚刚起步）。起初还是挺痛苦的，特别是数据库设计和查询，大学学习的东西基本都还回去了，不过在一次次问题中也渐渐总结了些经验，这里就记录一下“初学者”难免会遇到的一些问题。</p>
<a id="more"></a>
<h3 id="设置默认值"><a href="#设置默认值" class="headerlink" title="设置默认值"></a>设置默认值</h3><p>其实先处理模型，然后再根据模型建库和表，基本上没什么太大问题（毕竟都是可视化操作，不写 SQL 代码生成了）。不过，在可视化建表的过程中，有时候为了图快往往容易忽视一些配置，如：</p>
<ul>
<li>int 的默认值部分配置</li>
</ul>
<p><img data-src="/images/mysql-int-type.jpg" alt="int 类型"></p>
<ul>
<li>datetime 默认值部分配置</li>
</ul>
<p><img data-src="/images/mysql-datetime-type.jpg" alt="datetime 类型"></p>
<p>根据情况配置对应默认值可以减少代码内的部分重复操作，如：</p>
<ul>
<li>配置 <code>create_time</code> 默认值为 <code>CURRENT_TIMESTAMP</code>， 那么每次新增时就可以不用带上时间戳了。</li>
<li>配置 <code>modify_time</code> 默认值勾选上 “根据当前时间戳更新”，那么每次编辑时可以不用去配置修改时间，对于重复数据操作会比较方便。</li>
</ul>
<h3 id="日期更新"><a href="#日期更新" class="headerlink" title="日期更新"></a>日期更新</h3><p>当然，也有情况是需要在进行某些操作后，更新其它数据的一些信息，这之中比较麻烦的是“日期”相关的操作，在网上也没找到比较合适的博文来解决。这里在翻查了 Mysql 的一些函数，顺利解决了这么一个问题，修改数据时间的 <code>sql</code> 为：</p>
<figure class="highlight sql"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">update</span> xxx_table</span><br><span class="line"><span class="keyword">set</span> xxx_time = <span class="keyword">CURRENT_TIMESTAMP</span>()</span><br><span class="line"><span class="keyword">where</span> xxx_id = <span class="number">1</span></span><br></pre></td></tr></table></figure>
<p>配合 <code>mysql</code> 的时间函数能比较方便的处理时间相关的操作。</p>
<h3 id="ALTER-和-UPDATE-区别"><a href="#ALTER-和-UPDATE-区别" class="headerlink" title="ALTER 和 UPDATE 区别"></a>ALTER 和 UPDATE 区别</h3><p>最开始写 <code>sql</code> 时，总是习惯性的使用 <code>ALTER</code>，毕竟是 <code>ALTER</code> 是修改的意思嘛。实际上这两个区别很大，<code>ALTER</code> 是修改表结构的，而 <code>UPDATE</code> 是更新表数据信息的。因此在平时对数据进行 CRUD 时，记住使用 <code>UPDATE</code> 即可。这里记录一下：</p>
<ul>
<li><code>ALTER</code>、<code>DROP</code> 是结构上的更新和删除</li>
<li><code>UPDATE</code>、<code>DELETE</code> 是数据上的更新和删除</li>
</ul>
<h3 id="group-concat-的长度限制"><a href="#group-concat-的长度限制" class="headerlink" title="group_concat 的长度限制"></a><code>group_concat</code> 的长度限制</h3><p>在做函数聚合处理时，会经常使用到 <code>group_concat</code> 函数对字段进行聚合，但是 mysql 默认对聚合的字串设有长度限制（没记错的话应该是 1024）,这会导致在取值的时候对于比较长的字段就直接被截取掉了，还比较难发现问题。</p>
<p>对于自己的数据库，我们可以使用如下命令查看默认长度：</p>
<figure class="highlight sql"><table><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">show</span> <span class="keyword">variables</span> <span class="keyword">like</span> <span class="string">'group_concat_max_len'</span>;</span><br></pre></td></tr></table></figure>
<p>如果要修改其长度限制的话，有两种方法：</p>
<p><strong>（1）更改 Mysql 配置文件</strong></p>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br></pre></td><td class="code"><pre><span class="line"># 在配置文件中加入如下内容：</span><br><span class="line">group_concat_max_len = 1024000</span><br></pre></td></tr></table></figure>
<p><strong>（2）在 Navicat 内运行如下命令</strong></p>
<figure class="highlight sql"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">set</span> <span class="keyword">global</span> group_concat_max_len = <span class="number">1024000</span>;</span><br><span class="line"><span class="keyword">set</span> <span class="keyword">session</span> group_concat_max_len = <span class="number">1024000</span>;</span><br></pre></td></tr></table></figure>
<blockquote>
<p>注意： 该方法缺点是重启服务后设置失效</p>
</blockquote>
<h3 id="mysql-连接阻塞问题"><a href="#mysql-连接阻塞问题" class="headerlink" title="mysql 连接阻塞问题"></a>mysql 连接阻塞问题</h3><p>最近遇到搭建的测试环境报错，查看日志发现是 mysql 的 max_connect_errors 报错导致服务器 ip 被禁止连接 mysql。但是自己通过 navcat 能够连接上数据库，查了下原因，发现应该是中间有一版本的代码部署后，node 代码数据库连接部分配置失误，导致错误连接数过大，ip 被禁止连接 mysql 了，针对不同情况有不同的解决方法，这里都列举出来：</p>
<h4 id="max-connect-errors-值过小，容易出错"><a href="#max-connect-errors-值过小，容易出错" class="headerlink" title="max_connect_errors 值过小，容易出错"></a>max_connect_errors 值过小，容易出错</h4><p>通过 navicat 连接上 mysql，查询一下 mysql 的 <code>max_connect_errors</code> 属性是否值过小，较小时代码更新过程中容易产生 max_connect_errors 错误导致 mysql 连接不上，查询并更新方法如下：</p>
<figure class="highlight sql"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment"># 查询连接数</span></span><br><span class="line"><span class="keyword">show</span> <span class="keyword">variables</span> <span class="keyword">like</span> <span class="string">'%max_connect_errors%'</span>;</span><br><span class="line"></span><br><span class="line"><span class="comment"># 设置连接数</span></span><br><span class="line"><span class="keyword">set</span> <span class="keyword">global</span> max_connect_errors = <span class="number">1000</span>;</span><br></pre></td></tr></table></figure>
<h4 id="累计连接错误数超出"><a href="#累计连接错误数超出" class="headerlink" title="累计连接错误数超出"></a>累计连接错误数超出</h4><p>如果查询到的 <code>max_connect_errors</code> 数值已经比较大了，但是仍然报 <code>max_connect_errors</code> 超出的错误，那么应该是 mysql 的错误连接累计数量超出了，此时需要清空一下 <code>max_connect_errors</code> 数，在 navicat 的查询中输入：</p>
<figure class="highlight sql"><table><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">flush</span> <span class="keyword">hosts</span>;</span><br></pre></td></tr></table></figure>
<h4 id="mysql-的-max-connect-errors-重启后变小"><a href="#mysql-的-max-connect-errors-重启后变小" class="headerlink" title="mysql 的 max_connect_errors 重启后变小"></a>mysql 的 <code>max_connect_errors</code> 重启后变小</h4><p>因为 mysql 重启后会重新读取 mysql 的 conf 文件，如果不想每次重启 mysql 都需要重新更改 <code>max_connect_errors</code> 数值，那么需要修改一下 my.cnf 文件，将一下内容的值改改</p>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line">max_connect_errors = 1000</span><br></pre></td></tr></table></figure>
<h3 id="insert-数据重复问题"><a href="#insert-数据重复问题" class="headerlink" title="insert 数据重复问题"></a>insert 数据重复问题</h3><p>在插入数据时，有时候会碰到插入的数据重复，因此可以使用 <code>insert ... update ...</code> 语句来进行插入/更新。</p>
<p>使用语法大致如下：</p>
<figure class="highlight sql"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">insert</span> <span class="keyword">into</span> target_table(unique_col1, col2, col3)</span><br><span class="line"><span class="keyword">values</span> (val1, valb, valc), (val1, val2, val3)</span><br><span class="line"><span class="keyword">on</span> <span class="keyword">duplicate</span> <span class="keyword">key</span> <span class="keyword">update</span></span><br><span class="line">  col2 = <span class="keyword">values</span>(col2),</span><br><span class="line">  col3 = <span class="keyword">values</span>(col3)</span><br></pre></td></tr></table></figure>
<p>意思可理解为这样：</p>
<ul>
<li>当插入的 unique_col1 值不存在时，进行新增操作，其值分别对应为：(val1、val2、val3)</li>
<li>当插入的 unique_col1 值存在时，进行更新操作，分别更新 col2 和 col3 的值为传入 values 组对应的 val2 和 val3</li>
</ul>
<blockquote>
<p>注意，唯一值重复时，后面的数据会覆盖前面的数据内容（即只取最新数据）</p>
</blockquote>
<h3 id="参考文档"><a href="#参考文档" class="headerlink" title="参考文档"></a>参考文档</h3><ul>
<li><a href="https://www.runoob.com/mysql/mysql-functions.html" target="_blank" rel="noopener">MySQL 函数</a></li>
<li><a href="https://blog.csdn.net/weixin_39469127/article/details/93768427" target="_blank" rel="noopener">MySQL 中 insert into … on duplicate key update … values() 的使用笔记</a></li>
</ul>

    </div>

    
    
    
        

<div>
<ul class="post-copyright">
  <li class="post-copyright-author">
    <strong>本文作者： </strong>蔡胤
  </li>
  <li class="post-copyright-link">
    <strong>本文链接：</strong>
    <a href="https://monocy.gitee.io/2020/06/09/Mysql-的小技巧/" title="Mysql 的小技巧">https://monocy.gitee.io/2020/06/09/Mysql-的小技巧/</a>
  </li>
  <li class="post-copyright-license">
    <strong>版权声明： </strong>本博客所有文章除特别声明外，均采用 <a href="https://creativecommons.org/licenses/by-nc-sa/4.0/" rel="noopener" target="_blank"><i class="fab fa-fw fa-creative-commons"></i>BY-NC-SA</a> 许可协议。转载请注明出处！
  </li>
</ul>
</div>


      <footer class="post-footer">
          
          <div class="post-tags">
              <a href="/tags/数据库/" rel="tag"><i class="fa fa-tag"></i> 数据库</a>
              <a href="/tags/Mysql/" rel="tag"><i class="fa fa-tag"></i> Mysql</a>
          </div>

        


        
    <div class="post-nav">
      <div class="post-nav-item">
    <a href="/2020/04/28/在-typescript-中添加-webworker/" rel="prev" title="在 typescript 中添加 webworker">
      <i class="fa fa-chevron-left"></i> 在 typescript 中添加 webworker
    </a></div>
      <div class="post-nav-item">
    <a href="/2020/07/09/Linux-防火墙的使用和配置（转载）/" rel="next" title="Linux 防火墙的使用和配置（转载）">
      Linux 防火墙的使用和配置（转载） <i class="fa fa-chevron-right"></i>
    </a></div>
    </div>
      </footer>
    
  </article>
  
  
  



          </div>
          
    <div class="comments" id="valine-comments"></div>

<script>
  window.addEventListener('tabs:register', () => {
    let { activeClass } = CONFIG.comments;
    if (CONFIG.comments.storage) {
      activeClass = localStorage.getItem('comments_active') || activeClass;
    }
    if (activeClass) {
      let activeTab = document.querySelector(`a[href="#comment-${activeClass}"]`);
      if (activeTab) {
        activeTab.click();
      }
    }
  });
  if (CONFIG.comments.storage) {
    window.addEventListener('tabs:click', event => {
      if (!event.target.matches('.tabs-comment .tab-content .tab-pane')) return;
      let commentClass = event.target.classList[1];
      localStorage.setItem('comments_active', commentClass);
    });
  }
</script>

        </div>
          
  
  <div class="toggle sidebar-toggle">
    <span class="toggle-line toggle-line-first"></span>
    <span class="toggle-line toggle-line-middle"></span>
    <span class="toggle-line toggle-line-last"></span>
  </div>

  <aside class="sidebar">
    <div class="sidebar-inner">

      <ul class="sidebar-nav motion-element">
        <li class="sidebar-nav-toc">
          文章目录
        </li>
        <li class="sidebar-nav-overview">
          站点概览
        </li>
      </ul>

      <!--noindex-->
      <div class="post-toc-wrap sidebar-panel">
          <div class="post-toc motion-element"><ol class="nav"><li class="nav-item nav-level-3"><a class="nav-link" href="#前言"><span class="nav-number">1.</span> <span class="nav-text">前言</span></a></li><li class="nav-item nav-level-3"><a class="nav-link" href="#设置默认值"><span class="nav-number">2.</span> <span class="nav-text">设置默认值</span></a></li><li class="nav-item nav-level-3"><a class="nav-link" href="#日期更新"><span class="nav-number">3.</span> <span class="nav-text">日期更新</span></a></li><li class="nav-item nav-level-3"><a class="nav-link" href="#ALTER-和-UPDATE-区别"><span class="nav-number">4.</span> <span class="nav-text">ALTER 和 UPDATE 区别</span></a></li><li class="nav-item nav-level-3"><a class="nav-link" href="#group-concat-的长度限制"><span class="nav-number">5.</span> <span class="nav-text">group_concat 的长度限制</span></a></li><li class="nav-item nav-level-3"><a class="nav-link" href="#mysql-连接阻塞问题"><span class="nav-number">6.</span> <span class="nav-text">mysql 连接阻塞问题</span></a><ol class="nav-child"><li class="nav-item nav-level-4"><a class="nav-link" href="#max-connect-errors-值过小，容易出错"><span class="nav-number">6.1.</span> <span class="nav-text">max_connect_errors 值过小，容易出错</span></a></li><li class="nav-item nav-level-4"><a class="nav-link" href="#累计连接错误数超出"><span class="nav-number">6.2.</span> <span class="nav-text">累计连接错误数超出</span></a></li><li class="nav-item nav-level-4"><a class="nav-link" href="#mysql-的-max-connect-errors-重启后变小"><span class="nav-number">6.3.</span> <span class="nav-text">mysql 的 max_connect_errors 重启后变小</span></a></li></ol></li><li class="nav-item nav-level-3"><a class="nav-link" href="#insert-数据重复问题"><span class="nav-number">7.</span> <span class="nav-text">insert 数据重复问题</span></a></li><li class="nav-item nav-level-3"><a class="nav-link" href="#参考文档"><span class="nav-number">8.</span> <span class="nav-text">参考文档</span></a></li></ol></div>
      </div>
      <!--/noindex-->

      <div class="site-overview-wrap sidebar-panel">
        <div class="site-author motion-element" itemprop="author" itemscope itemtype="http://schema.org/Person">
    <img class="site-author-image" itemprop="image" alt="蔡胤"
      src="/images/avatar.jpg">
  <p class="site-author-name" itemprop="name">蔡胤</p>
  <div class="site-description" itemprop="description">Just do IT!</div>
</div>
<div class="site-state-wrap motion-element">
  <nav class="site-state">
      <div class="site-state-item site-state-posts">
          <a href="/archives/">
        
          <span class="site-state-item-count">61</span>
          <span class="site-state-item-name">日志</span>
        </a>
      </div>
      <div class="site-state-item site-state-categories">
            <a href="/categories/">
          
        <span class="site-state-item-count">15</span>
        <span class="site-state-item-name">分类</span></a>
      </div>
      <div class="site-state-item site-state-tags">
            <a href="/tags/">
          
        <span class="site-state-item-count">31</span>
        <span class="site-state-item-name">标签</span></a>
      </div>
  </nav>
</div>
  <div class="links-of-author motion-element">
      <span class="links-of-author-item">
        <a href="https://github.com/kazehaiya" title="GitHub → https://github.com/kazehaiya" rel="noopener" target="_blank"><i class="fab fa-github fa-fw"></i></a>
      </span>
      <span class="links-of-author-item">
        <a href="mailto:c763416559@163.com" title="Mail → mailto:c763416559@163.com" rel="noopener" target="_blank"><i class="fa fa-envelope fa-fw"></i></a>
      </span>
      <span class="links-of-author-item">
        <a href="https://weibo.com/Nora_Monocy" title="Weibo → https://weibo.com/Nora_Monocy" rel="noopener" target="_blank"><i class="fab fa-weibo fa-fw"></i></a>
      </span>
  </div>


  <div class="links-of-blogroll motion-element">
    <div class="links-of-blogroll-title"><i class="fa fa-link fa-fw"></i>
      友情链接
    </div>
    <ul class="links-of-blogroll-list">
        <li class="links-of-blogroll-item">
          <a href="http://liujinkai.com/" title="http://liujinkai.com/" rel="noopener" target="_blank">凯凯刘</a>
        </li>
        <li class="links-of-blogroll-item">
          <a href="https://weekly.75team.com/" title="https://weekly.75team.com/" rel="noopener" target="_blank">奇舞周刊</a>
        </li>
        <li class="links-of-blogroll-item">
          <a href="https://75.team/post/list" title="https://75.team/post/list" rel="noopener" target="_blank">奇舞团博客</a>
        </li>
        <li class="links-of-blogroll-item">
          <a href="https://tech.meituan.com/" title="https://tech.meituan.com/" rel="noopener" target="_blank">美团技术团队</a>
        </li>
        <li class="links-of-blogroll-item">
          <a href="https://tech.youzan.com/" title="https://tech.youzan.com/" rel="noopener" target="_blank">有赞技术团队</a>
        </li>
        <li class="links-of-blogroll-item">
          <a href="https://kalacloud.com" title="https://kalacloud.com" rel="noopener" target="_blank">卡拉云</a>
        </li>
    </ul>
  </div>

      </div>
        <div class="back-to-top motion-element">
          <i class="fa fa-arrow-up"></i>
          <span>0%</span>
        </div>

    </div>
  </aside>
  <div id="sidebar-dimmer"></div>


      </div>
    </main>

    <footer class="footer">
      <div class="footer-inner">
        

        
  <div class="beian"><a href="https://beian.miit.gov.cn" rel="noopener" target="_blank">京ICP备2020036147号-1 </a>
      <img src="/images/beian.png" style="display: inline-block;"><a href="http://www.beian.gov.cn/portal/registerSystemInfo?recordcode=42011702000651" rel="noopener" target="_blank">鄂公网安备 42011702000651 号 </a>
  </div>

<div class="copyright">
  
  &copy; 2018 – 
  <span itemprop="copyrightYear">2022</span>
  <span class="with-love">
    <i class="fa fa-dragon"></i>
  </span>
  <span class="author" itemprop="copyrightHolder">蔡胤</span>
    <span class="post-meta-divider">|</span>
    <span class="post-meta-item-icon">
      <i class="fa fa-chart-area"></i>
    </span>
      <span class="post-meta-item-text">站点总字数：</span>
    <span title="站点总字数">101k</span>
    <span class="post-meta-divider">|</span>
    <span class="post-meta-item-icon">
      <i class="fa fa-coffee"></i>
    </span>
      <span class="post-meta-item-text">站点阅读时长 &asymp;</span>
    <span title="站点阅读时长">1:32</span>
</div>

        








      </div>
    </footer>
  </div>

  
  <script src="/lib/anime.min.js"></script>
  <script src="//cdn.jsdelivr.net/gh/theme-next/theme-next-pjax@0/pjax.min.js"></script>
  <script src="//cdn.jsdelivr.net/npm/medium-zoom@1/dist/medium-zoom.min.js"></script>
  <script src="//cdn.jsdelivr.net/npm/lozad@1/dist/lozad.min.js"></script>
  <script src="/lib/velocity/velocity.min.js"></script>
  <script src="/lib/velocity/velocity.ui.min.js"></script>
<script src="/js/utils.js"></script><script src="/js/motion.js"></script>
<script src="/js/schemes/pisces.js"></script>
<script src="/js/next-boot.js"></script>
  <script>
var pjax = new Pjax({
  selectors: [
    'head title',
    '#page-configurations',
    '.content-wrap',
    '.post-toc-wrap',
    '.languages',
    '#pjax'
  ],
  switches: {
    '.post-toc-wrap': Pjax.switches.innerHTML
  },
  analytics: false,
  cacheBust: false,
  scrollTo : !CONFIG.bookmark.enable
});

window.addEventListener('pjax:success', () => {
  document.querySelectorAll('script[data-pjax], script#page-configurations, #pjax script').forEach(element => {
    var code = element.text || element.textContent || element.innerHTML || '';
    var parent = element.parentNode;
    parent.removeChild(element);
    var script = document.createElement('script');
    if (element.id) {
      script.id = element.id;
    }
    if (element.className) {
      script.className = element.className;
    }
    if (element.type) {
      script.type = element.type;
    }
    if (element.src) {
      script.src = element.src;
      // Force synchronous loading of peripheral JS.
      script.async = false;
    }
    if (element.dataset.pjax !== undefined) {
      script.dataset.pjax = '';
    }
    if (code !== '') {
      script.appendChild(document.createTextNode(code));
    }
    parent.appendChild(script);
  });
  NexT.boot.refresh();
  // Define Motion Sequence & Bootstrap Motion.
  if (CONFIG.motion.enable) {
    NexT.motion.integrator
      .init()
      .add(NexT.motion.middleWares.subMenu)
      .add(NexT.motion.middleWares.postList)
      .bootstrap();
  }
  NexT.utils.updateSidebarPosition();
});
</script>




  




  <script src="/js/local-search.js"></script>












    <div id="pjax">
  

  


<script>
NexT.utils.loadComments(document.querySelector('#valine-comments'), () => {
  NexT.utils.getScript('//cdn.jsdelivr.net/npm/valine@1/dist/Valine.min.js', () => {
    var GUEST = ['nick', 'mail', 'link'];
    var guest = 'nick,mail';
    guest = guest.split(',').filter(item => {
      return GUEST.includes(item);
    });
    new Valine({
      el         : '#valine-comments',
      verify     : true,
      notify     : true,
      appId      : 'GkgJm97N3UFm2mRb1eFcP2dn-gzGzoHsz',
      appKey     : 'kJ8tYUUkX4ifhWha8rjnxWS8',
      placeholder: "请不要吝惜你的笔头，来说点什么吧！",
      avatar     : 'mm',
      meta       : guest,
      pageSize   : '10' || 10,
      visitor    : false,
      lang       : 'zh-cn' || 'zh-cn',
      path       : location.pathname,
      recordIP   : true,
      serverURLs : ''
    });
  }, window.Valine);
});
</script>

    </div>
<script src="/live2dw/lib/L2Dwidget.min.js?094cbace49a39548bed64abff5988b05"></script><script>L2Dwidget.init({"pluginRootPath":"live2dw/","pluginJsPath":"lib/","pluginModelPath":"assets/","tagMode":false,"debug":false,"model":{"jsonPath":"/live2dw/assets/Epsilon2.1.model.json"},"display":{"position":"right","width":150,"height":300},"mobile":{"show":true,"scale":0.5},"react":{"opacity":0.7},"log":false});</script></body>
</html>
